Proponents of terraforming Mars — changing its environment to be more Earth-like in a way that would allow terrestrial life to survive without the need for life-support systems — propose releasing ‘greenhouse gases’ from a variety of sources on the planet to thicken the atmosphere and increase the temperature to the point where liquid water is stable on the surface.

“Carbon dioxide and water vapor are the only greenhouse gases that are likely to be present on Mars in sufficient abundance to provide any significant greenhouse warming,” said study lead author Dr. Bruce Jakosky, from the Laboratory for Atmospheric and Space Physics and the Department of Geological Sciences at the University of Colorado, Boulder.

Although studies investigating the possibility of terraforming Mars have been made before, the new result takes advantage of about two decades of additional spacecraft observations of the planet.

“These data have provided substantial new information on the history of easily vaporized materials like carbon dioxide and water on the planet, the abundance of volatiles locked up on and below the surface, and the loss of gas from the atmosphere to space,” said study co-author Dr. Christopher Edwards, of Northern Arizona University.

Dr. Jakosky and Dr. Edwards analyzed the abundance of carbon-bearing minerals and the occurrence of carbon dioxide in polar ice using data from NASA’s Mars Reconnaissance Orbiter and Mars Odyssey spacecraft, and used data on the loss of the Martian atmosphere to space by NASA’s MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft.

“Our results suggest that there is not enough carbon dioxide remaining on Mars to provide significant greenhouse warming were the gas to be put into the atmosphere; in addition, most of the carbon dioxide gas is not accessible and could not be readily mobilized. As a result, terraforming Mars is not possible using present-day technology,” Dr. Jakosky said.

Although Mars has significant quantities of water ice that could be used to create water vapor, previous analyses show that water cannot provide significant warming by itself; temperatures do not allow enough water to persist as vapor without first having significant warming by carbon dioxide.

Also, while other gases such as the introduction of chloroflorocarbons or other fluorine-based compounds have been proposed to raise the atmospheric temperature, these gases are short-lived and would require large-scale manufacturing processes, so they were not considered in the current study.

This infographic shows the various sources of carbon dioxide on Mars and their estimated contribution to the atmospheric pressure. Image credit: NASA’s Goddard Space Flight Center.

With Mars being further away from the Sun, researchers estimate a carbon dioxide pressure similar to Earth’s total atmospheric pressure is needed to raise temperatures enough to allow for stable liquid water.

The most accessible source is carbon dioxide in the polar ice caps; it could be vaporized by spreading dust on it to absorb more solar radiation or by using explosives. However, vaporizing the ice caps would only contribute enough carbon dioxide to double the Martian pressure to 1.2% of Earth’s, according to the new analysis.

Another source is carbon dioxide attached to dust particles in Martian soil, which could be heated to release the gas. The researchers estimate that heating the soil could provide up to 4% of the needed pressure.

A third source is carbon locked in mineral deposits. Using the recent NASA spacecraft observations of mineral deposits, they estimate the most plausible amount will yield less than 5% of the required pressure, depending on how extensive deposits buried close to the surface may be.

Just using the deposits near the surface would require extensive strip mining, and going after all the carbon dioxide attached to dust particles would require strip mining the entire planet to a depth of around 100 yards (91 m). Even carbon dioxide trapped in water-ice molecule structures, should such ‘clathrates’ exist on Mars, would likely contribute less than 5% of the required pressure.

Carbon-bearing minerals buried deep in the Martian crust might hold enough carbon dioxide to reach the required pressure, but the extent of these deep deposits is unknown, not evidenced by orbital data, and recovering them with current technology is extremely energy intensive, requiring temperatures above 572 degrees Fahrenheit (300 degrees Celsius).

Shallow carbon-bearing minerals are not sufficiently abundant to contribute significantly to greenhouse warming, and also require the same intense processing.

Another idea is to import volatiles by redirecting comets and asteroids to hit Mars. However, the team’s analysis reveals that many thousands would be required; again, not very practical.

Taken together, the results indicate that terraforming Mars cannot be done with present-day technology.

Source: Sci News